Diesel exhaust fluid formulation that reduces urea deposits in exhaust systems

ABSTRACT

A Diesel Exhaust Fluid (DEF) that includes urea, demineralized water and between 5 and 300 ppm formaldehyde, this formulation of DEF include less than 0.6 ppm of phosphates, calcium, iron, aluminum, magnesium, sodium, and potassium, the formulation also includes less than 0.3 ppm copper, zinc, chromium, and nickel. This formulation of DEF reduces the accumulation of urea deposit in the diesel exhaust system relative to other formulation of specification grade DEF that include less formaldehyde.

FIELD OF THE INVENTION

This invention relates generally to formulations of DEF that include lowlevels of formaldehyde and reduce the deposition of urea in the exhaustsystems of engines that use DEF requiring SCR catalysts.

BACKGROUND

Diesel engines are the preferred means of producing torque for use in awide range of applications ranging from uses in transportation such asheavy-duty trucks and trains, off-road agricultural and mining equipmentto the large scale production of on-site electrical power to name a few.Their virtually unmatched power to mass ratios and the relative safetyof their fuel makes them almost the only choice for use in applicationssuch as long-haul trucks, tractors, earth movers, combines, surfacemining equipment, non-electric locomotives, high capacity emergencypower generators and the like.

Diesel engines operate at high internal temperature. One consequence oftheir high operating temperatures is that at least some of the Nitrogenpresent in the engine at the moment of combustion may combine withOxygen to form NO_(x) including species such as NO and NO₂. Anotherconsequence of their high operating temperatures is that diesel exhaustat or near the point of exit from the engine is very hot.

A compound such as NO_(x) is problematic because it readily combineswith volatile organic compounds in the atmosphere to form smog. NO_(x)is regarded as a pollutant and virtually every industrialized nationregulates the levels of NO_(x) that can be legally discharged into theatmosphere. The regulation governing NO_(x) emissions are expected tobecome even more strict. Fortunately, engine and equipment manufacturershave developed systems for reducing the levels of NO_(x) produced by thecombustion of diesel fuel and released into the environment. Still, witheven tighter limits on the amounts of these compounds that can bereleased into the atmosphere there remains a need for improved materialsand methods for reducing the levels of NO_(x); some aspects of theinstant invention address this need.

SUMMARY

Some embodiments provide formulations of Diesel Exhaust Fluid (“DEF”)that includes about 32.5 wt. % urea at least 0.0010 wt. % formaldehyde,and demineralized water. The inventive formulations of DEF include lessthan 0.6 ppm of phosphates, calcium, iron, aluminium, magnesium, sodium,and potassium, the formulation also includes less than 0.3 ppm copper,zinc, chromium, and nickel.

In some embodiments, the DEF formulation includes about 0.005 wt. %formaldehyde. Still other embodiment include between about 0.0010 wt. %to about 0.3 wt. % formaldehyde.

In some embodiments, the formulation comprises between about 15.0 wt. %to about 40.0 wt. % urea; between about 15.0 wt. % to about 40.0 wt. %ammonium carbamate; at least 0.0010 wt. % formaldehyde, and betweenabout 40.0 wt. % to about 60.0 wt. % water.

Some embodiments include formulations for reducing oxides of nitrogen,comprising: between about 19.0 wt. % to about 30.0 wt. % urea; betweenabout 15.0 wt. % to about 40.0 wt. % ammonium carbamate; at least 0.0010wt. % formaldehyde; and between about 40.0 wt. % to about 60.0 wt. %water. In some embodiments the formulations include: between about 19.0wt. % to about 25.0 wt. % urea; between about 20.0 wt. % to about 35.0wt. % ammonium carbamate; at least 0.0010 wt. % formaldehyde; andbetween about 45.0 wt. % to about wt. 55.0% water. And in still otherembodiments the formulations include between about 19.0 wt. % to about22.0 wt. % urea; between about 30.0 wt. % to about 35.0 wt. % ammoniumcarbamate; at least 0.0010 wt. % formaldehyde; and between about 45.0wt. % to about 50.0 wt. % water.

Yet other embodiments include methods for reducing an oxide of nitrogen,comprising the steps of: providing a formulation, wherein theformulation includes: urea, ammonium carbamate and demineralized waterand is suitable for use in Selective Catalytic Reduction (“SCR”) ofNO_(x). In some embodiments, the formulation comprises between about15.0 wt. % to about 40.0 wt. % urea; between about 15.0 wt. % to about40.0 wt. % ammonium carbamate; at least 0.0010 wt. % formaldehyde, andbetween about 40.0 wt. % to about 60.0 wt. % water.

Yet other embodiments include adding ammonium carbamate as a readilysoluble powder to a tank that already includes standard DEF. In someembodiments, these methods include the step of supplying pre-packagedquantities of powdered ammonium carbamate which can be added to areductant tank that includes urea. In some embodiments, these methodsinclude the step of determining the composition of the reductant toinsure that the relative levels of water, urea and ammonium carbamate inthe reductant system are suitable for use in SCR and the new mixturesexhibit lower freezing temperatures than conventional DEF.

In some embodiments, the methods for reducing oxides of nitrogen includethe steps of supplying at least one SCR catalyst and contacting the SCRcatalyst with said formulation. Some embodiments include the step ofmeasuring the composition of said formulation. While still otherembodiments include the further step of adding a portion of ammoniumcarbamate to a formulation of reductants.

Some embodiments provide DEF formulations suitable for use in methodsand/or systems that reduce NO_(x) exhaust emissions that include betweenabout 15.0 wt. % to about 40.0 wt. % urea; between about 15.0 wt. % toabout 40.0 wt. % ammonium carbamate; between about 0.0010 wt. % to about0.3 wt. % formaldehyde; and between about 40.0 wt. % to about 60.0 wt. %water.

Yet other embodiments include systems for reducing an oxide of nitrogenin an engine exhaust, comprising the steps of: a formulation thatincludes a reductant wherein the formulation includes: between about19.0 wt. % to about 30.0 wt. % urea; between about 15.0 wt. % to about40.0 wt. % ammonium carbamate; between about 0.0010 wt. % to about 0.01wt. % formaldehyde; and between about 40.0 wt. % to about 60.0 wt. %water; a SCR catalysts, where the catalyst catalyses the reduction ofNO_(x) by said reductant to form products that include N₂.

In some embodiments, the systems for reducing NO_(x) emissions include:reductant formulations having between about 19.0 wt. % to about 25.0 wt.% urea; between about 20.0 wt. % to about 35.0 wt. % ammonium carbamate;between about 0.0010 wt. % to about 0.010 wt. % formaldehyde; andbetween about 45.0 wt. % to about wt. 55.0% water. In some embodiments,the formulations in the systems includes: between about 19.0 wt. % toabout 22.0 wt. % urea; between about 30.0 wt. % to about 35.0 wt. %ammonium carbamate; between about 0.0010 wt. % to about 0.3 wt. %formaldehyde; and between about 45.0 wt. % to about 50.0 wt. % water.

Some embodiments include methods for making spec grade Diesel ExhaustFluid that has a final level of formaldehyde in the range of 0.001 wt. %to about 0.01 wt. %, or 0.002 wt. % to about 0.01 wt. %, or 0.005 wt. %to about 0.01 wt. %, or 0.001 wt. % to about 0.05 wt. %, or 0.0023 wt. %to about 0.01 wt. %, or 0.0023 wt. % to about 0.006 wt. %, or 0.001 wt.% to about 0.005 wt. %, or 0.001 wt. % to about 0.004 wt. %, or 0.001wt. % to about 0.006 wt. %, these methods include adding a source offormaldehyde such as formalin to Diesel Exhaust Formulation such thatthe amount of formaldehyde added to the DEF is between about 0.06 wt %to about 1.0 wt. %, or 0.06 wt % to about 0.80 wt. %, or 0.06 wt % toabout 0.60 wt. %, or 0.06 wt % to about 0.50 wt. %, or about 0.06 wt %to about 0.4 wt. %, or 0.1 wt % to about 1.0 wt. %, or 0.1 wt % to about0.8 wt. %, or 0.1 wt % to about 0.6 wt. %, or 0.1 wt % to about 0.5 wt.%, or 0.1 wt % to about 0.4 wt. %, or about 0.10 wt. % to about 0.30 wt.% of the final formulation of DEF.

Some embodiments include methods and/or systems for adding formaldehydeto urea based diesel exhaust formulation. Methods for addingformaldehyde include bubbling or sparging gaseous formaldehyde in anaqueous preparation of exhaust treatment grade urea. Other methodsincluding adding liquid preparations of that include formaldehyde suchas formalin to aqueous solution of exhaust treatment grade urea. Theseadditions can be made in bulk supplies before the diesel exhaustformulation is dispersed to individual pieces of equipment. In stillother embodiments, individual pieces of equipment can be outfitted witha formaldehyde reservoir that is connected so as to deliver formaldehydedirectly into the equipment's onboard DEF storage tank or to beco-administered along with DEF directly into the diesel exhaust system.

BRIEF DESCRIPTION OF THE FIGURES

FIG. 1. Schematic diagram of a representative SCR exhaust treatmentsystem for a diesel engine.

FIG. 2. A graph of grams (g) of urea deposited in diesel exhaust systemas function of the wt. % of formaldehyde added to spec DEF.

FIG. 3. A schematic showing portions of an exemplary diesel exhausttreatment system.

DESCRIPTION

For the purposes of promoting an understanding of the principles of thenovel technology, reference will now be made to the preferredembodiments thereof, and specific language will be used to describe thesame. It will nevertheless be understood that no limitation of the scopeof the novel technology is thereby intended, such alterations,modifications, and further applications of the principles of the noveltechnology being contemplated as would normally occur to one skilled inthe art to which the novel technology relates are within the scope ofthis disclosure and what it claims.

Unless implicitly intended or explicitly stated otherwise, the term,“about” as used herein refers to a range of values including plus orminus 10 percent of the stated value, for example, about 1.0 encompassesthe range of values 0.9 to 1.1.

As used herein the term “demineralized water” refers to water thatincludes very low levels of minerals in general, and in particular verylow levels of sulfur, alkaline metals, earth metals, vanadium, arsenic,ash, or any other compounds that are known to damage SCR catalysts.Demineralized water for use in the inventive formulations can be made byany method known in the art for reducing the level of contaminants indemineralized water including distillation and reverse osmosis.

Most industrialized nations set limits on the levels of NO_(x) that canbe released into the atmosphere by diesel engines. In the United States,the Environmental Protection Agency (EPA) is the agency of the federalgovernment responsible for regulating diesel engine exhaust emissions.The EPA has proffered new regulations governing the levels of NO_(x)that can be legally discharged into the atmosphere by diesel enginespowering off-road equipment. These new regulations are referred to as“Final Tier 4.” The EPA's Final Tier 4 standards require that dieselengines which are operated off-road limit their NO_(x) emissions to nomore than 0.4 g/kW-h.

Currently available technology used to reduce the amount of NO_(x)emission emitted from diesel exhaust fumes includes Selective CatalyticReduction (SCR). This technology is widely used to reduce NO_(x)emissions from heavy duty diesel engines and takes advantage of the hightemperatures found in diesel exhaust fumes. Typical chemical reactionscatalyzed by SCR catalysts are the reduction of NO_(x) such as NO₂ or NOto N₂ and H₂O. In SCR based exhaust treatment systems, the oxidizedforms of Nitrogen are reacted with compounds such as ammonia (NH₃). Someof the reactions that occur on the surface of the SCR catalyst includethe following:

Diesel Exhaust Fluid (DEF) is a formulation comprising about 32.5 wt. %urea in demineralized water. DEF is widely used to reduce NO and NO₂ toN₂ in a reaction that takes place on the surface of the SCR catalyst.

A typical SCR catalyst comprises a large surface area and includes aninert heat substrate that is coated with at least one stable catalyticmaterial. Substrates used in such catalysts include ceramic materials;typical catalytic materials include metals and/or metal oxides such ascopper, iron, vanadium, and the like. The particular combination ofcatalytic surface material and substrate for use in a particularapplication depends in part on a number of factors such as thecomposition fuel being combusted including, for example, the amount ofsulphur in the fuel, the temperature of the exhaust gases, the levels ofNO_(x) reduction desired, the reductant being used, the levels and typesof other compounds present in the exhaust fumes and the like.

Anhydrous ammonia exists predominately as a gas under ambient conditionswhile aqueous ammonia is formed by contacting ammonia with water.Anhydrous ammonia is difficult to handle and dangerous if not properlycontained. Ammonia carrier such as urea is safer and easier to handle,store and transport than anhydrous ammonia. Urea plus water exists inliquid form at standard temperature and pressure. DEF is an especiallyuseful reductant for use in mobile applications since it is easier tohandle, store and transport than anhydrous ammonia. Accordingly, DEF isa commonly used reductant in SCR diesel exhaust treatment systems usedin mobile applications such as heavy trucks and off-road constructionand agricultural equipment.

In a typical SCR based exhaust treatment system, an SCR catalyst ispositioned in the exhaust stream of a diesel engine. The catalyst ispositioned such that the temperature of the exhaust fumes contacting thesurface of the catalyst is high enough to sustain the reaction of theNO_(x) in the exhaust fumes with the reductant but not so high that theheat produced by the engine and the chemical reactions that take placein the exhaust stream damages the catalyst.

Referring now to FIG. 1, a schematic diagram of a typical heavy dutydiesel exhaust treatment system (2). An SCR catalyst (4) is positionedwithin an exhaust pipe (6). The exhaust pipe has two ends. One end (8)is connected to a source of NO_(x) (10) and the other end (12) is ventedto the atmosphere (14). A typical system may also include an optionadditional pair of catalysts, (16) and (18), these are positioned before(16) and after (18) the SCR catalyst (4). The oxidation catalystscatalyse the oxidation of various compounds in the exhaust streamincluding organic molecules and un-reacted ammonia.

Because the SCR system requires a reductant such as ammonia or urea, theSCR system includes a system for storing, and delivering the reductantto the catalyst. Still referring to FIG. 1, reductant storage vessel(20) is connected to a first delivery tube (22). First delivery tube(22) has two ends the first end the inlet (24) of tube (22) is connectedto storage vessel (20) while the second end the outlet (26) of tube (22)is connected to a reductant delivery valve (28) that regulates the flowof the reductant from tube (22) to a second delivery tube (30). Tube(30) also has two ends the first end inlet (32) is connected to theoutlet of valve (28) while the second end outlet (34) of second deliverytube (32) is connected to the exhaust pipe (6). The outlet (34) ofsecond delivery tube (30) is connected to exhaust pipe (6) such that thereductant in second delivery tube (30) is delivered onto or near thesurface of SCR catalyst (4) by outlet (34).

In some embodiments, the SCR system (2) may include a device (36) formaintaining the temperature of the reductant in storage vessel (20). Insome configurations, the first reductant delivery tube (22), thereductant delivery value (28) and/or the second reductant delivery tube(30) may also be equipped with a device (40) to help regulate thetemperature of the reductant in the system. In some embodiments of theinvention, the device for regulating the temperature of the reductant(40) may be selected from the group consisting of: insulation, a heatingcoil or sock; and/or a cooling or warming jacket or some combinationthereof.

In some embodiments, the system (2) may further include an optionalmixing device (43) supplied to either periodically or continuouslyagitate the contents of reductant storage vessel (20). Vessel (20) mayalso be equipped with a temperature sensor (44) to measure thetemperature of the contents of vessel (20). Vessel (20) may also beequipped with a probe (46) for measuring the nitrogen content of thematerial stored in vessel (20). In some embodiments, the system may besupplied with a controller (42) which may include inputs from sensorsconnected to the exhaust and/or SCR systems. The controller may also beequipped with a Central Processing Unit or dedicated logic circuits thatregulate the dispersion of reductant to the system as necessary tomaintain the release of NO_(x) within acceptable limits. The controllermay also be used to monitor the temperature or the reductant deliverysystem and perhaps to control portions of the system dedicated tomaintain the reductant within an acceptable temperature range. In someembodiments, the same controller is used to regulate the rate and/orfrequency of the agitator associated with reductant storage tank one. Insome embodiments, the controller may be used to monitor the level ofreductant and/or the composition of the reductant in reductant storagevessel (20). Some exhaust systems include an oxidation catalyst (18),generally located downstream of the SCR catalyst. Some oxidativecatalysts can oxidize ammonia and formaldehyde, thereby preventing therelease of these compounds into the atmosphere.

Sensors that can be used to monitor the level of compounds that includeammonia and urea in DEF formulation include, but are not limited, tothose disclosed in U.S. Pat. No. 7,722,813 issued on May 25, 2010, whichis incorporated herein by reference in its entirety. Some of thesesensors operate by measuring the ability of a formulation of DEF totransfer heat and correlating this property with the concentration ofurea in the system. In some versions the sensor in the form of a probeis inserted into the DEF formulation. In some embodiments, the systemincludes a circuit used to supply a current applied to a heating elementpositioned in a portion of the probe that is submerged in the DEF inorder to produce heat and a temperature sensing device that is alsosubmerged in the DEF. The amount of current that must be applied to theheating element in order to produce a discernable effect on thetemperature sensor is influenced by the composition of the liquidsurrounding the probe tip. The relationship between the levels ofcurrent that must be applied to affect a temperature change measured atthe probe's temperature sensor can be determined as a function of ureacontent in the DEF. Once the relationship between current and ureacontent is known for a given probe and a formulation with certaincomponents the relationship can then be used to infer the level of ureain a sample of DEF by measuring the amount of current required to effecta change in temperature. Any method that can be used to determine or atleast estimate the composition of DEF in a storage tank or anywhere in aSCR system can be used to practice the invention.

Spec grade DEF is widely available for use in SCR based NO_(x) reductionsystems. Spec grade DEF includes on the order of about 32.5 wt. % ureaand purified water. These formulations are optimized to prolong catalystlife and include extremely low levels of impurities that can causedeposits or poison expensive SCR catalysts. Accordingly, SCR spec gradeDEF and the formulations disclosed herein have virtually undetectablelevels of sulphur, metals, non-combustible fillers, other inertcontaminants, compounds whose effects on SCR catalyst life are unknown.

This technology is well known and has widespread use in Europe, and itsuse has been growing in North America. Still some challenges persist inthe use of this technology including the tendency for urea deposits toform in the exhaust system especially between the DEF dosing inlet andupstream of selective catalytic reduction (SCR) catalyst and therelatively high freezing point of 32.5 wt. % urea in water solutions.This latter problem has been addressed by certain formulationnitrogen-based reductants which have lower freezing points than aqueousurea and still function. Some of these formulations are disclosed inU.S. patent application Ser. No. 13/193,793 filed on Jul. 29, 2010, thedisclosure of which is incorporated herein by reference in its entirety.

The problem of urea deposition in the DEF feeding system can causereduced fuel efficiency, particulate filter failure, damage to the SCRcatalyst bed, and even engine failure as a significant build-up of ureain the exhaust system may cause excessive back pressure. Some exhaustsystems are equipped with pressure sensors, in part to detect theeffects of urea deposition. These sensors are part of a monitoringsystem that enables the diesel operator to detect problematic ureabuild-up and to take appropriate action such as shutting down the systemuntil the deposits can be physically removed from the system. Stillother systematic approaches to addressing the problem of urea build-upis to alter the position the DEF feed tube and/or time the release ofDEF into portion of the exhaust system immediately up-stream of the SCRcatalytic bed in order to minimize the time that urea rich DEF is incontact with the DEF feed system and pre-SCR section of the exhaustsystem.

Some aspects of the instant invention address the problem of ureadeposition by introducing small amount of formaldehyde into DEF. Theseformulations exhibit an unexpectedly lower tendency to form ureadeposits without an apparent effect of SCR catalytic efficiency. Asdisclosed herein, the addition of small amount of formaldehyde on theorder of 0.03 wt. % to spec grade DEF can reduce the urea deposition.Embodiments of the invention include spec. grade DEF mixed with at least0.08 wt. % formaldehyde, for use in the catalytic reduction of NO_(x) indiesel engine exhaust.

Aspects of the invention include formulation of spec grade DEF thatinclude levels of formaldehyde sufficient to significantly reduce thelevel of urea deposited in the diesel exhaust treatment system. Many ofthese formulations, much like currently commercially available specgrade DEF, is substantially fee any compound that can affect SCRperformance and half-life.

Still other aspects of the invention include introducing urea and levelsof formaldehyde sufficient to reduce the deposition of urea in thediesel exhaust system by 90, 95, or even 98 or greater percent thatsimilar DEF formulation that do not include the levels of formaldehydedisclosed herein.

Methods for adding formaldehyde directly to spec grade DEF include anymethod for the addition of such compounds to aqueous solutions. Thesemethods include bubbling or sparing gaseous formaldehyde into aqueouspreparations of spec grade DEF in the level of formaldehyde in the DEFreach the desired levels. Such mixing can be done when DEF ismanufactured or it may be down sometime later, for example, when DEF isadded to DEF container in the commercial outlet or in the tank or othercontainer that hold spec grade DEF.

Still another method for adding formaldehyde to DEF is to mix liquidpreparations of formaldehyde directly with spec grade DEF. In someembodiments, the formaldehyde mixed with the spec grade DEF is itself inthe mixture of compounds. One such preparation of formaldehyde that canbe mixed with DEF is formalin, a mixture of formaldehyde, methanol, andwater.

Still another method for using formaldehyde to reduce urea build-up indiesel exhaust systems is to introduce formaldehyde into the mixer alongwith spec grade DEF. Some of these methods may make use formaldehyde'slow vapour pressure (formaldehyde is a gas at room temp with high vapourpressure up to 5 bar). In some embodiments, a high pressure cartridgethat includes formaldehyde is used to deliver the requisite level offormaldehyde into a DEF storage tank located at the commercial outletwhere spec grade DEF is solid or into a DEF reservoir position on theequipment. One advantage of this approach is that it eliminates or atleast reduces the customer's exposure to formaldehyde.

EXAMPLES

Referring now to Table 1. Various formulation of DEF were created andtested to determine if the different formulations had a measurableeffect on the tendency of urea to deposit in a disease exhaust treatmentsystem. The engine run parameters used to generate the data summarizedin Table 1, are presented in Table 2.

Referring again to Table 1. As a control and to determine a base linefor urea deposition in the system used to test various formulation ofDEF, commercially available DEF was tested. The DEF tested, included32.5 wt. % urea; a sample of this material was analyzed and was found toinclude 0.0005 wt. % aldehyde.

The required quantities of spec DEF (commercially available) andformalin (mixture of water, formaldehyde and methanol) were added andmixed well in a sealed container with a help of magnetic stirrer. Thesealed container was placed in 31° C. water bath prior to being tested.

Referring next to FIG. 3, a schematic of an exemplary diesel exhaustsystem (100) is illustrated. Diesel exhaust system (100) illustrativelyincludes exhaust inlet (102), DOC (104), DPF (106), doser (108),decomposition tube (110), mixer (112), SCR/SCR-AOC (114), and exhaustoutlet (116). SCR/SCR-AOC (114) may be an SCR or a combination of an SCRand an oxidation catalyst. The amount of urea that may be deposited inthe exhaust treatment system is a function of factors including engineoperating parameters, ambient condition, the positioning and/orconfiguration of the doser (108), and/or mixer (112) with thedecomposition tube (110). Referring now to FIG. 2, the effect of doserand mixer on the rate of urea deposition is illustrated by thedifferences in the amount of urea deposited as shown by the 2 differentcurves in the figure. In both arrangement the addition of small amountsof formaldehyde to the DEF reduced the rate at which urea was depositedin the diesel exhaust treatment system.

The decomposition tube in aftertreatment system, where one would expecturea to be deposited, was removed and recorded for clean weight at 250°C. The decomposition tube was then installed back into the system beforethe urea deposit study was started. Prior to injecting the modified DEFinto the decomposition tube, circulating coolant was used to maintainthe temperature of the dosing module at about 80° C. The test wascarried out with a help of flow bench set-up which mimics exact engineconditions. Desired steady state space velocity and stable temperatureswere achieved with help of air flow and natural gas combustionrespectively. Under specific flow bench and steady state conditions, therequired quantities of modified DEF injected into decomposition tube for4 hrs (See Table 2). Once the test was completed, the decomposition tubewas removed and weighed at 250C. The amount of urea deposited in thetube was calculated based on initial and final weight of decompositiontube. The amount of urea in the various formulations and the amount ofurea deposited in the decomposition tube is summarized in Table 1.

Other formulations that were made and tested for their effect on ureadeposition included: 0.11 wt. % methanol, added to specification gradeDEF (spec DEF); 0.32 wt. % formic acid added to spec DEF; 0.32 wt. %,0.16 wt. %, 0.08 wt. %, or 0.03 wt. % formalin added to spec DEF. Theaddition of defined amounts of formalin to DEF resulted in a change inthe amount of formaldehyde measured in the various mixtures.

TABLE 1 Mixtures of DEF and various additives, level of formaldehydemeasured in the various mixtures, the amount of urea (g) deposited in atest diesel exhaust treatment system. Resulting urea formalde- ureadeposit Solution mixture of Spec Added hyde deposit reduction DEF andAdditive wt % (wt %) (g) by (%) DEF** —  0.0005 @ 190 0.0 Methanol inspec DEF 0.11 NA 185.6 2.3 Formic acid in spec DEF 0.32 NA 200.1 −5.3Formaldehyde in spec DEF 0.32  0.0050 @ 0.9 99.5 Formaldehyde in specDEF 0.16  0.0023 @ 1.5 99.2 Formaldehyde in spec DEF 0.08 0.0010 * 43.677.1 Formaldehyde in spec DEF 0.03 0.0005 * 117.5 38.2 **All mixtures inTable 1 include specification-grade DEF, which comprises about 32.5%urea. @ determined by chemical analysis * Expected values Note:formaldehyde was added to spec DEF by measured amounts of Formalin, amixture of formaldehyde (35-39%), methanol(10-15%) and water. Resultsreported in the table are those obtained using doser A & mixer A.

TABLE 2 Engine Test Conditions used to collect the data summarized inTable 1. Steady Test Condition State Exhaust flow (kg/hr) 350 Exhaustflow temp (C.) 350 DEF flow (g/sec) 0.38 Test duration (hr) 4

Referring now to FIG. 2. Some of the data in Table 1 is presentedgraphically (see lower line in the figure). The upper curve shows thepercent of urea accumulation as a function of formaldehyde in the DEFused in the test (doser A and mixer A). The curve generated with doser Band mixer B (the upper curve) illustrates 1) the effect of doser andmixer choice and position on the rate of urea deposition and 2) thatless urea accumulates in the exhaust system with either doser and mixercombination when formaldehyde is added to the DEF.

While the novel technology has been illustrated and described in detailin the figures and foregoing description, the same is to be consideredas illustrative and not restrictive in character, it being understoodthat only the preferred embodiments have been shown and described andthat all changes and modifications that come within the spirit of thenovel technology are desired to be protected. As well, while the noveltechnology was illustrated using specific examples, theoreticalarguments, accounts, and illustrations, these illustrations and theaccompanying discussion should by no means be interpreted as limitingthe technology. All patents, patent applications, and references totexts, scientific treatises, publications, and the like referenced inthis application are incorporated herein by reference in their entirety.

We claim:
 1. A formulation for reducing oxides of nitrogen in dieselengine exhaust, comprising: about 19.0 wt. % to about 40 wt. % urea; atleast 0.0010 wt. % formaldehyde; and demineralized water.
 2. Theformulation according to claim 1, including: no more than 0.6 ppm ofphosphates, calcium, iron, aluminum, magnesium, sodium and potassium;and no more than 0.3 ppm copper, zinc, chromium, and nickel.
 3. Theformulation according to claim 2, comprising: between about 0.001 wt. %and about 0.01 wt. % formaldehyde.
 4. The formulation according to claim2, further including: between about 15.0 wt. % to about 40.0 wt. %ammonium carbamate.
 5. The formulation according to claim 4, comprising:between about 19.0 wt. % to about 35.0 wt. % urea; between about 15.0wt. % to about 40.0 wt. % ammonium carbamate; at least 0.0010 wt. %formaldehyde; between about 40.0 wt. % to about 60.0 wt. % demineralizedwater; no more than 0.6 ppm of phosphates, calcium, iron, aluminum,magnesium, sodium and potassium; and no more than 0.3 ppm copper, zinc,chromium, and nickel.
 6. The formulation according to claim 5, whereinsaid formulation comprises: between about 19.0 wt. % to about 35.0 wt. %urea; between about 20.0 wt. % to about 35.0 wt. % ammonium carbamate;between about 0.0020 wt. % to about 0.01 wt. % formaldehyde; betweenabout 45.0 wt. % to about wt. 55.0% demineralized water.
 7. Theformulation according to claim 5, wherein said formulation comprises:between about 19.0 wt. % to about 22.0 wt. % urea; between about 30.0wt. % to about 35.0 wt. % ammonium carbamate; between about 0.0050 wt. %to about 0.01 wt. % formaldehyde; and between about 45.0 wt. % to about50.0 wt. % demineralized water.
 8. A method for reducing an oxide ofnitrogen in diesel exhaust, comprising the steps of: providing a DieselExhaust Fluid formulation, wherein the formulation includes: urea;ammonium carbamate; formaldehyde; demineralized water; no more thanabout 0.6 ppm of phosphates, calcium, iron, aluminum, magnesium, sodium,and potassium; and no more than 0.3 ppm copper, zinc, chromium andnickel, wherein said formulation is suitable for use in the SelectiveCatalytic Reduction of NOx in diesel engine exhaust gases; andintroducing the formulation into diesel exhaust such that theformulation reacts with NOx on the surface of a SCR.
 9. The methodaccording to claim 8, wherein said formulation, comprises: between about15.0 wt. % to about 40.0 wt. % urea; between about 15.0 wt. % to about40.0 wt. % ammonium carbamate; between about 40.0 wt. % to about 60.0wt. % demineralized water; and between about 0.001 wt. % to about 0.010wt. % formaldehyde.
 10. The method according to claim 8, wherein saidformulation, comprises: between about 19.0 wt. % to about 35.0 wt. %urea; between about 15.0 wt. % to about 40.0 wt. % ammonium carbamate;and between about 40.0 wt. % to about 60.0 wt. % demineralized water.11. The method according to claim 8, wherein said formulation,comprises: between about 19.0 wt. % to about 22.0 wt. % urea; betweenabout 30.0 wt. % to about 35.0 wt. % ammonium carbamate; and betweenabout 45.0 wt. % to about 50.0 wt. % demineralized water.
 12. The methodaccording to claim 8, further including the step of: determining thecomposition of said formulation.
 13. The method according to claim 12,wherein the determining step includes measuring the amount of urea insaid formulation.
 14. The method according to claim 13, wherein thedetermining step includes using a sensor and wherein the sensor is incontact with said formulation.
 15. The method according to claim 8,further including the step of: adjusting the composition of saidformulation by the addition of at least one chemical to saidformulation, wherein the at least one chemical is selected from thegroup consisting of: urea, ammonium carbamate, formaldehyde, anddemineralized water.
 16. A system for reducing the level of NOx releasedinto the atmosphere by the combustion of diesel fuel; comprising aformulation, wherein said formulation includes: urea; ammoniumcarbamate; formaldehyde; and demineralized water; wherein saidformulation is suitable for the Selective Catalytic Reduction of NOx indiesel exhaust gases; and a reservoir for holding at one component ofsaid formulation.
 17. The system according to claim 16, wherein theformulation, comprises: between about 15.0 wt. % to about 40.0 wt. %urea; between about 15.0 wt. % to about 40.0 wt. % ammonium carbamate;between about 0.0010 wt. % to about 0.010 wt. % formaldehyde; andbetween about 40.0 wt. % to about 60.0 wt. % demineralized water. 18.The system according to claim 16, wherein said formulation comprises:between about 19.0 wt. % to about 35.0 wt. % urea; between about 20.0wt. % to about 35.0 wt. % ammonium carbamate; between about 0.0020 wt. %to about 0.01 wt. % formaldehyde; and between about 45.0 wt. % to aboutwt. 55.0% demineralized water.
 19. The system according to claim 16,wherein said formulation comprises: between about 19.0 wt. % to about22.0 wt. % urea; between about 30.0 wt. % to about 35.0 wt. % ammoniumcarbamate; between about 0.0020 wt. % to about 0.05 wt. % formaldehyde;and between about 45.0 wt. % to about 50.0 wt. % demineralized water.20. The system according to claim 17, further including: a device formeasuring the composition of said formulation.